1. Field of the Invention
The present invention relates to stage units and exposure apparatuses, and more particularly to a stage unit that is suitable as a stage that sets the position of a specimen of an exposure apparatus or other precision instruments, and to an exposure apparatus that is equipped with the stage unit.
2. Description of the Background Art
Conventionally, in a lithography process for manufacturing a semiconductor device, a liquid crystal display device or the like, exposure apparatuses such as a reduction projection exposure apparatus by a step-and-repeat method (the so-called ‘stepper’) that transfers a pattern formed on a mask or a reticle (hereinafter generally referred to as a ‘reticle’) onto a substrate such as a wafer or a glass plate (hereinafter also referred to as a wafer as needed) that is coated with a resist or the like, or a scanning exposure apparatus by a step-and-scan method (a scanner) are mainly used.
In these types of exposure apparatuses, due to higher integration of semiconductor devices and finer pattern accompanying therewith, further improvement in resolution of a projection optical system has been required. Therefore, a wavelength of an exposure light has been shortened year by year and an exposure apparatus using an ArF excimer laser beam has also been in practical use. The resolution and a device rule required for an exposure apparatus become further stricter in the future without fail, which recently leads to the situation where an EUV exposure apparatus (EUVL) that uses an SOR (Synchrotron Orbital Radiation) ring, a laser plasma light source, or the like that emits an extreme ultraviolet (EUV) light having a wavelength equal to or less than 100 nm as an exposure light source draws the attention. Meanwhile, conventionally, when a fine pattern, for example, an original circuit pattern is drawn on a reticle blank, an electron beam exposure apparatus has been relatively frequently used.
In the stepper, the scanner or the like, a wafer stage is driven in XY two-dimensional directions by, for example, a drive unit including a linear motor or the like, in order to transfer a reticle pattern on a plurality of shot areas on a wafer. In particular, in the scanner, in order for a reticle stage and a wafer stage to perform acceleration, constant speed and deceleration respectively upon exposure, the vibration caused by a reaction force generated at a linear motor stator due to the acceleration/deceleration adversely affects the apparatus, in particular, an optical system, which causes the decrease in exposure accuracy. Therefore, any reaction force processing mechanism is indispensable. However, since the reticle stage only has to be movable back and forth only in a scanning direction, the reaction force and the vibration in the drive direction are easily processed on one axis, and a counter mass reaction processing mechanism using the law of conservation of momentum that is used most in general for mass production exposure apparatuses can be easily applied to (e.g. refer to Kokai (Japanese Unexamined Patent Application Publication) No. 08-063231 and the U.S. Pat. No. 6,246,204). On the contrary, since the wafer stage moves in the X-axis and Y-axis directions in a long stroke as described above, the reaction processing cannot be performed easily, and in order to realize the reaction processing, in some cases, a stage structure needs to be devised.
In the recent ultraviolet exposure apparatus (irrespective of whether an immersion type or not), since a degree of cleanliness of a main section in which exposure is performed needs to be maintained at a very high level, for example, at nearly Class 1, for example, in the case of ArF excimer laser exposure apparatus or the like, a main section of the exposure apparatus is covered by a chamber that is called as an environmental chamber and the inside of the chamber is isolated from the outside so that a clean state is maintained. Further, since an EUV light is absorbed by almost all substances, an optical path space of an EUV light needs to be set to a predetermined high vacuum state, and in a normal EUV exposure apparatus, an optical path of an exposure light as a matter of course, and a movement space of a wafer stage that moves while holding a wafer need to be set to a vacuum state. Therefore, the wafer stage is placed in a vacuum chamber. Besides, in an electron beam exposure apparatus, a wafer stage needs to be placed in a vacuum chamber in order to deflect a beam to a desired direction.
Thus, in a present-day exposure apparatus, regardless of the types, a wafer stage is placed in a chamber, and therefore, in the case a conventional counter mass mechanism is employed, a counter mass (hereinafter referred to as a ‘counterweight’) that moves a distance in a direction opposite to a drive direction of the stage in accordance with a drive distance of the stage needs to be placed within the chamber. In this case, in order to shorten a movement stroke of the counterweight, a heavy weight and large size counterweight needs to be housed within the chamber and the inner volume of the chamber has to be increased. On the other hand, when decreasing the size and weight of the counterweight, a movement distance of the counterweight becomes longer when receiving a reaction force at the time of driving the wafer stage, and as a consequence, the inner volume of the chamber in which the counterweight is housed has to be increased. In either case, the chamber tends to be larger in size.
For example, in an ArF excimer laser exposure apparatus or the like, the increase in size of the chamber leads to the increase in size of an air supply fan, a cooler, a heater, an air filter and the like that constitute an air-conditioner, and to the increase in power consumption, and for example, in an EUV exposure apparatus and an electron beam exposure apparatus, leads to the increase in size of a vacuum pump and other vacuum-related instruments and the increase in power consumption.
Also in an apparatus other than an exposure apparatus, the similar inconvenience occurs as far as the apparatus houses a stage inside a chamber or a space partitioned by a partition wall.